The aims of this project are: (1)\to study the structure-function relationships in the alpha-fetoprotein (AFP) molecule, making use of the proteolytic fragments and monoclonal antibodies reactive with various parts of the AFP molecule; (2)\to use the monoclonal antibodies reactive with carbohydrate-bearing fragments of AFP in the development of assays specific for the concanavalin A molecular variants of human AFP; and (3)\to study the usefulness of monoclonal antibodies in immunolocalization of AFP-producing tumors. During the past year, these studies have focused on the suitability of AFP as a target antigen for monoclonal antibody-toxin conjugates. We have also initiated studies on the structure of the carbohydrate in hepatoma cell-derived AFP. We have developed a tumor model using the AFP producing the hepatoma cell line HepG2 to study the effect of monoclonal antibody-ricin A chain conjugates on these cells. Monoclonal anti-placental alkaline phosphatase (PLAP) and tumor cells that have PLAP at their surface have been used as a complementary test system. We have shown that anti-PLAP conjugates are cytotoxic to the cells carrying PLAP, but that anti-AFP conjugates are not cytotoxic in this system. AFP shows an interesting and potentially important variation in its carbohydrate moiety. We have previously shown that AFP isolated from fetal bovine serum (liver-derived AFP) has a concanavalin A nonbound fraction, which carries one or two triantennary oligosaccharides. In contrast, as demonstrated by others, the concanavalin A nonbinding fraction of AFP in the amniotic fluid (yolk sac-derived AFP) has a bisecting N-acetyl glucosaminyl structure. It is, therefore, possible that the concanavalin A nonbound AFP fraction made by yolk sac and yolk sac tumors differs from the concanavalin A nonbound AFP fraction made in the liver and by hepatomas. In order to be able to compare these AFPs in the same species, we have started working on the AFP produced by the HepG2 hepatoma cells. We have found that the HepG2 liver cancer cells make AFP, which has a large concanavalin A nonbinding fraction, and that we can isolate large enough quantitites of this AFP for chemical analysis. In functional studies on AFP, the transfer of fatty acids by AFP from or to cells will be studied by using a serum-free culture system with cultured cells. These studies may help clarify the physiological role of AFP in the fetus and will generate reagents useful in tumor diagnosis and possibly even therapy. (A)